First CH3D detection in Class 0/I proto-brown dwarfs: constraints on CH4 abundances

ABSTRACT We report the first detection in JK = 10–00 rotational transition line of CH3D towards three Class 0/I proto-brown dwarfs (proto-BDs) from IRAM 30-m observations. Assuming a temperature 25 K, abundances (relative to H2) are range (2.3–14.5) × 10−7. The CH4 derived and assuming DCO+/HCO+ ratios (0.05–4.8) 10−5. gas-phase formation via CH2D+ is enhanced at high densities 108–1010 cm−3 our observations likely probing innermost dense warm regions proto-BDs. Thermal and/or non-thermal desorption can return molecules formed an early stage on grain surfaces gas-phase. indicative carbon-chain chemistry proto-BDs where synthesized lukewarm (∼20–30 K) region close central source.